Compression molding using a self-aligning and activating mold system

ABSTRACT

A compression molding system and method, including a mold set and one or more hydraulic cylinders that create a self-aligning and self-activating operating unit. The hydraulic cylinders can include a combination of activation and clamping cylinders. The mold set includes a first and second mold section and a source of heat is provided to heat the mold set. The mold sections are constructed of individual plates or bar stock, and machined to define a mold cavity. Reinforcement plates can be attached to the mold sections and add structure and integrity to the system. A computer control system interprets data from the activation hydraulic cylinders and monitors and controls hydraulic fluid flow into and out of each cylinder and a pumping system pumps hydraulic fluid into and out of the chambers within the activation and clamping cylinders.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of Ser. No. 10/492,924,filed Apr. 14, 2004, and claims priority benefits to InternationalApplication Serial No. PCT/US02/32590, filed Oct. 11, 2002, which is acontinuation-in-part of U.S. non-provisional application Ser. No.09/982,902 entitled “Hydraulic Pressure Forming Using a Self Aligningand Activating Die System,” filed Oct. 18, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to compression molding, andspecifically to compression molding using a self-aligning and activatingmold system and method.

2. Discussion of the Prior Art

Various molding processes exist to produce both simple and complexshapes having a wide range of geometry and thickness. Two existingprocesses are compression molding and resin transfer molding.

Compression molding converts uncured (un-exposed to heat) thermosetsheet molding compounds (SMC) known in the art into various products byapplying pressure in a closed mold that is heated to cure (set) the SMC.SMC molding typically includes a compression mold mounted into ahydraulic press of sufficient tonnage to generate adequate internalforce to cause the heated SMC material to flow and fill the mold. Inuse, a charge (material to be formed) of SMC is placed on a lowersection of a mold set. The press is closed under controlled conditionsto bring the two mold sections together resulting in compression moldingof the SMC. These systems typically require a molding pressure ofbetween 750 psi (53 bar) to 1500 psi (103 bar) to adequately flow thecompound and fill the mold cavity. The molds are typically heated toaround 290° F. to 310° F. to complete the cure (set) of the thermosetresin used in the SMC material. The mold/press remains closed and underpressure during the cure cycle. The duration of the cure cycle isdetermined by part thickness. A typical cure time for a 0.125 inch thickpart would be between 60 and 90 seconds.

Currently, a high tonnage compression press is required to generate themolding pressures necessary to form a standard SMC part. These pressesrequire special installation and deep foundations of reinforced concreteand can weigh many tons and can be over twenty (20) feet in height.Because of their large size and weight, the presses are usuallyassembled in one facility, disassembled, and then shipped in sectionsand re-assembled on-site. This increases overall costs and start-uptimes.

Thus, conventional SMC presses are expensive and therefore require along-term investment. Molds (tools) used in a conventional SMCcompression process are similarly expensive due to the requiredstructural integrity necessary to handle the high molding pressures. Themolds are typically machined from at least two rectangular solid steelbillets. These billets are engineered to withstand the high pressures ofcompression molding. Billet machining can remove as much as fiftypercent of the original material, thus adding to the overall cost of themold design. Because of the size and expense of SMC compression moldingoperations, SMC part production is usually restricted to high volumeparts (e.g., more than 50,000 units annually). Mid and low volumeproduct runs are often prohibitively expensive to produce using thistechnology.

A second conventional molding process is resin transfer molding (RTM).RTM injects a liquid thermoset resin into a heated or unheated moldcavity containing a dry glass preform (such as sheets of woven glassmaterial or fiberglass) and allowed to solidify (or cure) into a desiredpart shape. RTM is common and widely used in industry.

In use, RTM systems typically have upper and lower mold halves. Thesehalves are usually separated using a chain hoist. Once open, the dryglass preform is placed into the mold cavity. The mold halves are thenplaced back together and the preform is sealed within the mold halves.The resin is injected into the mold cavity, impregnating the preform.The pressure needed to complete the injection is typically 50 psi (3.5bar). The resin can then cure at either room temperature or apredetermined elevated temperature depending on the desired rate ofcure. Once the mixture has solidified, the mold is opened and the partis removed.

Resin transfer molds typically have a thin nickel tool surface backed byepoxy. The structural elements that support the tool surface can includea combination of plywood, fiberglass and steel. RTM tools areconstructed at relatively low cost when compared to SMC compressionmolds since little structural integrity is needed to handle itsrelatively low molding pressures (50 psi compared to 1000 psi in SMCsystems). In addition, the RTM process uses no press and has limitedinfrastructure costs.

Though relatively inexpensive, RTM has many limitations that make theprocess undesirable. These include a frequent inability to make a finalshape part; a relatively long cycle time; multi-phase operations areoften required; very operator skill dependent; part geometrylimitations; limited ability to achieve class A surface finish (i.e.visible or show surface); and part-to-part inconsistency. Given theabove limitations, RTM is mainly used for very low production volumes,non-class A surface parts, and simple shapes.

It would be advantageous to overcome the limitations of the RTM systemswithout the expense and structural requirements of the conventional SMCsystems. New SMC compounds have recently been developed that mold atmuch lower pressures (e.g., between 75 psi to 350 psi). These are nowproducts known in industry as low pressure molding compounds (LPMC) andlow pressure sheet molding compounds (LPSMC) which are sold respectivelyunder the trademarks CRYSTIC IMPREG made by Scott Bader Company Ltd ofNorthamptonshire, England and SMC-LITE made by Ashland SpecialtyChemical Company (Composite Polymers Division) of Columbus, Ohio. Suchcompounds include glass fiber composite impregnated with polyesterresins or low viscosity resins including isophthalic and orthosphthalicresins and the like. A new system and method, combining the simplicityand cost effectiveness of an RTM system with the part consistency andclass A finish capability of the SMC compression mold process is nowpossible for molding the new LPMC and LPSMC materials.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a compression moldingapparatus and method using a self-aligning and activating mold (SAAM)system. The present invention uses fabricated steel molds to mold thenew low pressure molding compounds (LPMC) and low pressure sheet moldingcompounds (LPSMC). Using a fabricated mold set integrated to a series ofhydraulic cylinders to create a self-contained operating unit, thesystem eliminates the need for a solid steel tool/mold set operated by aconventional high tonnage hydraulic press.

In one embodiment of the present invention an apparatus for compressionmolding includes a mold set having first and second mold sections and asource of heat for the mold set. At least one activation cylinder ismounted to either the first mold section or the second mold section andhas a retraction chamber and an extension chamber. The activationcylinder further includes a cylinder rod having an end mounted to theother of the first and second mold sections.

In another embodiment of the present invention a method of compressionmolding is provided using an apparatus that includes a mold set havingfirst and second mold sections and a source of heat for the mold set. Atleast one activation cylinder is mounted to one of the first and secondmold sections. The activation cylinder includes a retraction chamber andan extension chamber, and further includes a first cylinder rod havingan end mounted to the other of the first and second mold sections. Atleast one clamping cylinder is mounted to one of the first and secondmold sections. The clamping cylinder includes a second retractionchamber, a second extension chamber, and a second cylinder rod having asecond end releasably mounted to the other of the first and second moldsections. The method includes heating the mold set; placing a charge ofmaterial to be formed on one of the first and second mold sections;moving one of the mold sections towards the other mold section;actuating the second cylinder rod to meet the one mold section andactuating a lock member to releasably hold the second cylinder rod endto the one mold section; and pressing the mold sections together at apredetermined pressure for a predetermined time to mold the charge ofmaterial.

In another embodiment of the present invention a method of compressionmolding is provided using an apparatus including a mold set having afirst and second mold section, and a source of heat for the mold set. Atleast one activation cylinder is connected to one of the mold sections.The activation cylinder includes a retraction chamber, an extensionchamber, and further includes a cylinder rod having a cylinder rod endmounted to the other of the mold sections. The method comprises thesteps of heating the mold set; placing a charge of material to be formedon one of the mold sections; moving one mold section towards the othermold section; and pressing the mold sections together at a predeterminedpressure for a predetermined time to mold the charge of material.

While most mold sets of this invention are oriented so as to use upperand lower sections to benefit from the force of gravity in insertion ofmoldable material in the lower mold section, it will be understood thatthe invention is equally applicable to configurations wherein thesections are positioned in a side-by-side orientation (See FIG. 13).Thus, it should be understood that the invention contemplates the use offirst and second mold sections irrespective of their orientation, andthat the use of the terms “upper” and “lower” herein is for illustrativepurposes and for ease of understanding, only, and should not be deemedto limit the scope of the invention to any particular orientation of themold sections.

Other advantages and features of the present invention will become moreapparent to persons having ordinary skill in the art to which thepresent invention pertains from the following description taken inconjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing advantages and features, as well as other advantages andfeatures will become apparent with reference to the description andfigures below, in which like numerals represent like elements and inwhich:

FIG. 1 is a perspective view of a compression molding system of thepresent invention;

FIG. 2 is a side view of a fabricated mold set of the present inventionbefore the mold cavity is machined;

FIG. 3 is a side view of a fabricated mold set of the present inventionmachined to a desired work piece shape;

FIG. 4 is a side view of a fabricated mold set of the present inventionincluding reinforcement plates;

FIG. 5 is a side view of the compression molding system of the presentinvention including a clamping hydraulic cylinder and an activationhydraulic cylinder;

FIG. 6 is a compression mold system of the present invention in an openposition;

FIG. 7 is an alternate embodiment of the present invention using fouractivation cylinders;

FIG. 8A is a plan view of the alternate embodiment in FIG. 7;

FIG. 8B is a sectional view cut through line 8B-8B in FIG. 8A;

FIG. 9 illustrates steps of a compression mold system of the presentinvention in an open position loading a charge, a closed positionmolding the charge, and in an open position removing the molded charge;

FIG. 10 illustrates an alternate embodiment of the present inventionhaving one activation cylinder;

FIGS. 11A & 11B illustrate a top view of FIG. 10 and a sectional viewcut through line 11B-11B in FIG. 11A respectively;

FIG. 12 illustrates an alternate embodiment of the present inventionincluding four activation cylinders and two clamping cylinders.

FIG. 13 illustrates of the present invention mounted on a truck havingactivation and clamping cylinders.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a compression molding system thatcombines the advantages of the conventional sheet molding compound (SMC)systems with the resin transfer molding systems (RTM) while eliminatingknown disadvantages of each of these systems. The present inventionreplaces both the large solid steel mold set mounted to a conventionalhigh tonnage hydraulic SMC press and instead uses a fabricated orbar-stock mold set integrated to a series of strategically placedhydraulic cylinders and optional reinforcement plates.

Generally, the present invention is a self-contained, self-aligning andself-activating molding (SAAM) system 20 capable of developing thepressure required for compression molding of new low pressure moldingcompounds (LPMC) and other similar materials that have low pressuremolding and curing capabilities. The new LPMC material changes state(such as to a liquid) when heated thereby requiring less pressure tomold a shaped part. The present invention achieves the desired moldingcapabilities in a smaller, lighter and less expensive package comparedto conventional SMC molding systems. It is also an improvement over theRTM system in that the limitations of the RTM system as outlinedpreviously, are eliminated.

The present invention can be operated on a typical six-inch reinforcedconcrete factory floor, eliminating the need for a larger concrete padas required by conventional SMC molding systems. The working height ofthe new SAAM molding system 20 can be designed to suit the operators byaltering the location of the activation cylinders and defining thedesired height of the support pillars. The system 20 can be assembled,tested, demonstrated and approved in one facility and shipped assembledto the manufacturing plant as a “turn-key” operation. Thus, the systemprovides a cost advantage through reduced capital cost, and a fastertime for set up and production.

The major components of the molding system 20 of the present inventionare the mold set, hydraulic cylinders, hydraulic pumping system, andsystem controller. FIG. 1 illustrates an embodiment of the presentinvention utilizing a plurality of mold sets and cylinders connectedtogether. Alternate embodiments of the present invention demonstratevariations in the types of application available by varying the numberand configuration of the types of hydraulic cylinders, the mold setshape and the orientation of the molding apparatus. The apparatus of thepresent invention can be oriented horizontally or vertically dependingon the particular application.

FIG. 2 illustrates the mold sections of a mold set before the moldsections have been machined. The mold sections can include a pluralityof individual plates or a plurality of solid steel bar-stock 16,connected together in various shapes and sizes to form a mold set theshape and size of a desired part. The plates (or bar-stock) 16 can bemade of steel or any other material capable of supporting the forcesgenerated during the molding process for a given application. The plates(or bar-stock) 16 may be pre-formed to the approximate part shape bymethods such as bending, rolling, flame/gas cutting, and forging. Theplates (or bar-stock) 16 may be connected together along their perimeterusing conventional means such as welding, as shown by weld points 26, orbolting (not shown). Once connected, the plates 16 form a lower moldsection 22 and an upper mold section 24. The mold sections 22 and 24 arethen machined to create a desired mold cavity 25 corresponding to thepart to be molded (FIG. 5). Conventional methods such as milling orcomputer numerically controlled (CNC) machining can be used to machinethe mold sections. This mold set replaces the need to machine the moldfrom a single steel billet.

Most mold sets of this invention are oriented to use a lower moldsection and an upper mold section to benefit from the force of gravityin insertion of moldable material in the lower mold section. It will beunderstood that the invention is equally applicable to configurationswherein the mold sections are positioned in a side-by-side orientation(See FIG. 13). Thus, it should be understood that the inventioncontemplates the use of first and second mold sections irrespective oftheir orientation, and that the use of the terms “upper” and “lower”herein is for illustrative purposes and for ease of understanding, only,and should not be deemed to limit the scope of the invention to anyparticular orientation of the mold sections.

The mold sections 22 and 24 can also include a heat cavity 43 configuredto receive a heating element, which may be, for example, a resistanceheater, or, preferably a heated fluid medium such as hot oil or steam(FIG. 2). A conventional pumping unit 87 can be used to heat and pumpsteam or oil into and out of the heat cavities 43 (FIG. 1). Theparticular heat cavity 43 shown in the figures is representative of thetype of cavity required for use of steam as a heating medium. If hot oilis being used, a smaller cavity design will suffice. The heating mediumis pumped into the heat cavities 43 through heat ports 45 and heats themold sections 22 and 24 to the required temperature needed to mold aparticular work piece (FIGS. 11A & B).

The molding system 20 can be supported by a plurality of support pillars14 to place the molding system 20 at a height convenient for a typicalworker. The support pillars 14 can be affixed on one end to the lowermold section 22 using conventional methods such as bolting or welding.The opposite end of the support pillars 14 can be mounted to the floorusing conventional methods such as lag bolts. The support pillars 14support the weight of the system 20 and securely fasten the system 20 tothe floor to prevent it from moving and reduce excessive vibrationduring operation. FIGS. 1 and 7 show two different types of supportpillars 14, but any number of other possible support pillarconfigurations could also be used.

FIG. 3 illustrates the machined mold surfaces 32 and 33 of mold sections22 and 24. The machined mold surfaces 32 and 33 represent the shape ofthe part to be molded and define the mold cavity 25. Surfaces 32 and 33can also be surface finished by conventional means known in the art(e.g., repairing, detailing, grinding, sanding, and polishing) to createan acceptable production surface finish. Mating perimeter surfaces 34and 35 of the upper and lower mold sections serve to define theperiphery of mold cavity 25 and are oriented parallel to each other.

FIG. 4 illustrates the mold sections 22 and 24 including reinforcementplates 36, activation hydraulic cylinder mounting plate 38, clampinghydraulic cylinder mounting plate 39, activation hydraulic cylinder rodend mounting plate 40, and clamping hydraulic cylinder rod end mountingplate 41, all of which are mounted to the mold sections 22 and 24 usingconventional means such as welding or bolting. The illustratedembodiment shown in FIG. 1 is shown with six sets of reinforcementplates 36 (a first set on each upper mold section 24 and a second set oneach lower mold section 22). The reinforcement plates 36 providestrength and stability to the molding system 20 and can vary inquantity, shape, size and location depending on the size and particularembodiment of the molding apparatus. Stopping blocks 37 can be mountedto either the perimeter surface 34 of lower mold section 22 or perimetersurface 35 of upper mold section 24 and are used to set the gap betweenthe upper and lower mold sections 22 and 24 by stopping the moldsurfaces 32 and 33 from contacting each other. The thickness of the partto be molded may be dictated by the size of the stopping blocks 37. Thestopping blocks 37 can be various shapes and sizes depending on theparticular mold system design and for the particular part to be molded.

FIG. 5 illustrates an embodiment of the present invention where the moldsections 22 and 24 are connected to an activation hydraulic cylinder 42and a clamping hydraulic cylinder 44. The activation cylinder 42 canraise and lower the upper mold section 24 to allow convenient removal ofa work piece. The clamping cylinder 44 allows for additionalreinforcement to maintain the mold set in a closed position duringoperation.

The activation hydraulic cylinder 42 is mounted to the activationhydraulic cylinder mounting plate 38 on the lower mold section 22 andthe clamping hydraulic cylinder 44 is mounted to the clamping hydrauliccylinder mounting plate 39 on the lower mold section 22. The activationhydraulic cylinder 42 has a first cylinder rod 46 attached to a firstpiston 60. First cylinder rod 46 has a first cylinder rod end 48 that isfixedly mounted to the activation hydraulic cylinder rod end mountingplate 40 on the upper mold section 24 and extends slidably through aclosely fitting aperture in plate 38. The activation hydraulic cylinder42 includes two chambers defined as a first retraction chamber 62 and afirst extension chamber 64. Chambers 62 and 64 can have one or morefluid entry and exit points 80. Fluid is pumped to and from the firstretraction and extension chambers 62 and 64 to provide the clamping andextension force needed to move upper mold section 24 to and from lowermold section 22 using a conventional pumping system 86 and computercontrol system 56 (such as a Position Linear Control (PLC) illustratedin FIG. 1).

The clamping hydraulic cylinder 44 has a second cylinder rod 50 attachedto a second piston 66. The second cylinder rod 50 has a second cylinderrod end 52 that extends into and through the clamping hydraulic cylinderrod end mounting plate 41 and is configured to releasably lock intoposition into a rod end slide coupler unit 54. In the preferredembodiment, the clamping hydraulic cylinder rod end mounting plate 41includes the rod end slide coupler unit 54, which is configured toreceive the second cylinder rod end 52. FIG. 5 illustrates the rod endslide coupler unit 54 in its closed position locking the second cylinderrod end 52 securely in position. The rod end slide coupler unit 54engages when the upper mold section 24 reaches a predetermined pauseposition. Preferably, the predetermined pause position is when the uppermold section 24 is within approximately 25-50 mm of the lower moldsection 22.

The clamping hydraulic cylinder 44 has two chambers defined as a secondretraction chamber 68 and a second extension chamber 70. Each chamber 68and 70 can have one or more second fluid entry and exit points 82. Fluidcan be pumped to and from the second retraction and second extensionchambers 68 and 70 using the pumping system 86 and PLC control system56. The clamping hydraulic cylinder 44 assists in providing the clampingand extension forces needed to hold the upper and lower mold sections 22and 24 together during the molding process.

FIG. 6 illustrates the embodiment shown in FIG. 5 in an open positionwith the rod end slide coupler unit 54 shown in its open position. Whenthe mold sections 22 and 24 are in an open position, a part loading andremoval zone 58 is created. With the rod end slide coupler unit 54 inits open position, the second cylinder rod end 52 can be removed fromthe clamping hydraulic cylinder rod end mounting plate 41, and the firstcylinder rod 46 can be extended to raise the upper mold section 24. Whenupper mold section 24 is closing towards lower mold section 22, thefirst cylinder rod 46 and second cylinder rod 50 provide sufficientforming/closing pressure to mold the part within the mold cavity 25.Pressure typically remains constant during the complete curing stage.

In the illustrated embodiment shown in FIGS. 5 & 6, the clampinghydraulic cylinder 44 assists the activation hydraulic cylinder 42 inholding the mold sections 22 and 24 in a closed position duringoperation. The activation hydraulic cylinder 42 in combination with theclamping hydraulic cylinder 44 generate the clamping force required tokeep mold sections 22 and 24 together and under pressure during themolding and curing stages. Only the activation hydraulic cylinder 42controls the movement of mold section 24 away from mold section 22 toallow for part removal.

In summary, the clamping hydraulic cylinders 44 differ from activationhydraulic cylinders 42 in four ways. First, as stated above, theclamping hydraulic cylinders 44 provide clamping force only to hold themold sections 22 and 24 together during the molding stage. The clampinghydraulic cylinders 44 do not aid in raising and lowering the upper moldsection 24. Second, the clamping hydraulic cylinders 44 have a uniquelatching mechanism (the rod end slide coupler unit 54). By comparison,the activation hydraulic cylinders 42 have a fixed attachment on thefirst cylinder rod ends 48. Third, the clamping hydraulic cylinders 44allow unfettered ingress and egress of the charge/part because thesecond cylinder rod 50 does not reach into the charge/partloading/unloading zone 58 and can be retracted out of the way. Finally,the clamping hydraulic cylinders 44 are more economical, since secondcylinder rod 50 has a shorter stroke.

In an alternate embodiment (FIGS. 7 & 8), a system 20′ using the presentinvention includes only four activation hydraulic cylinders 42 and noclamping hydraulic cylinders 44. The activation hydraulic cylinders 42can open the mold sections 22′ and 24′ to allow insertion and removal ofthe molded parts and provide the required pressure for molding of apart. In this embodiment, the system 20′ is inverted in that theactivation hydraulic cylinders 42 are attached to a top side of theupper mold section 24′. The activation cylinder rod end 48 is fixedlyattached to the lower mold section 22′ instead of the upper mold section24′. As the upper mold section 24 moves away from the lower mold section22′ during operation, the activation cylinders 42 move with the uppermold section 24′. Reinforcement plates 36′ are included in thisembodiment and are positioned on the sides and exterior of the moldsections 22′ and 24′. These optional reinforcement plates 36′ addstrength and stability of the system in configurations where higherpressures are indicated.

In another embodiment, the system 20″ includes only one activationhydraulic cylinder 42 and no clamping hydraulic cylinders 44 (FIGS.10-11). In this embodiment, the cylinder 42 is positioned centrally todistribute the load equally and insure that the perimeter surfaces 34″and 35″ of upper and lower mold sections 22″ and 24″ remain parallelduring operation. This embodiment is similarly inverted with theactivation cylinder 42 being attached to the topside of the upper moldsection 24″. This type of single activation system would be used forcompression molding of smaller components that require less pressure.The smaller size of the system would also eliminate the need forreinforcement plates 36 used in the previous embodiments.

FIG. 12 illustrates another embodiment of the molding system 20′″ of thepresent invention. This configuration illustrates four activationcylinders 42 and two clamping cylinders 44. FIG. 13 illustrates a mobileembodiment 20″″ of the present invention where the molding system ismounted to a truck to provide for the ability to locate the moldingprocess at a desired remote 5 location. In this embodiment the moldingsystem is oriented horizontally and is mounted to the truck on tracks toallow the mold sections to slide along the tracks as they move togetherand apart during operation. This embodiment illustrates a compressionmolding system of the present invention having one activation cylinder42 and one clamping cylinder 44.

The activation hydraulic cylinders 42 and clamping hydraulic cylinders44 of the present invention are typically arranged on the periphery ofthe mold tool set except as illustrated in FIGS. 10 and 11. In theillustrated embodiments of FIGS. 1, 7 & 12, the activation hydrauliccylinders 42 and the clamping hydraulic cylinders 44 are placedsymmetrically around the mold set. The activation hydraulic cylinders 42and clamping hydraulic cylinders 44 can be placed in a wide range ofalternative layouts to suit the specific molding conditions andparameters as well as sound engineering requirements. The activationhydraulic cylinders 42 and clamping hydraulic cylinders 44 can be placedin an alternating layout or the cylinders 42 and 44 can be in anopposing layout where all the activation cylinders 42 are one side andthe clamping cylinders 44 are on the opposite side of the particularsystem. The key to configuring cylinder 42 and 44 placement is tomaintain an equal distribution to limit vertical and side molddeflection caused by pressure during production, and keep the upper moldsection 24 parallel to the lower mold section 22.

The movement of each activation hydraulic cylinder 42 can be monitoredby linear transducers (not shown), which are encased in the body of eachactivation hydraulic cylinder 42. The transducers transmit continuouslinear position data to the computer control system (PLC) 56 in FIG. 1.The PLC 56 interprets incoming data from all the activation hydrauliccylinders 42 in a given system. The PLC 56 also monitors and controlshydraulic fluid flow into and out of each activation hydraulic cylinder42 and clamping hydraulic cylinder 44 via valves at each cylinder'sfluid entry and exit points 80 and 82. The PLC 56 can also control theoperation of the clamping hydraulic cylinders 44 when they are includedin the system. The PLC 56 insures uniform speed, position, andself-alignment of the first cylinder rods 46 so that the upper and lowermold sections 22 and 24 always remain parallel and aligned with eachother.

The molding system 20 of the present invention is designed to meet theindividual needs of a specific part to be molded. Therefore, the forcesacting on the mold sections 22 and 24 must be calculated for a specificconfiguration. First, the surface area of the part is calculated. Next,the maximum pressure required to mold the part is determined. Theproduct of surface area and maximum required molding pressure determinesthe tonnage required for the particular molding system (surface area %required molding pressure=tonnage). Required molding pressure can varyfrom part to part depending on the complexity and geometry of the part,the depth of draw and desired finish. Steeper and deeper draw parts withthin wall thickness will require higher molding pressures. The typicalpressures for the present invention range between 70 psi (5 bar) and 150psi (11 bar) when using LPMC, but may increase to 350 psi (27 bar) forLPSMC products.

Hydraulic cylinders must also be evaluated to determine their outputforce. Output force is a function of the effective area of thecylinders. The cylinder's effective area is calculated using the formulafor piston area (cylinder bore) minus the rod diameter area (effectivearea=piston area−rod diameter). The total output force of the activationhydraulic cylinders 42 and clamping hydraulic cylinders 44 is specifiedto exceed the molding force.

The method of using the molding system 20 of the present inventionutilizing an activation hydraulic cylinder 42 in combination with aclamping hydraulic cylinder 44 as shown in FIGS. 1, 5 & 6, will now bedescribed. Alternative methods can be employed depending on theparticular embodiment (described above) to be used. The compressionmolding process begins with the mold sections 22 and 24 in the openposition and heated to approximately 300 degrees Fahrenheit. The heatingprocess is achieved by injecting hot oil or steam through ports 45 andinto heat cavities 43 positioned just below the mold surfaces 32 and 33(FIGS. 8B & 11B). A pre-weighed charge (usually a sheet of material) ofa low-pressure molding compound (LPMC) is placed in position on thelower mold section 22. The PLC 56 commands the molding sequence toinitiate. Fluid is pumped out of the first extension chamber 64 and intothe first retraction chamber 62 causing the mold sections 22 and 24 toclose.

When the upper mold section 24 reaches the predetermined pause position,(approximately 25 to 50 mm depending on the charge and moldingparameters) from the lower mold section 22, the clamping hydrauliccylinder 44, second cylinder rod end 52 and slide coupler unit 54 areengaged to assist the activation hydraulic cylinder 42 in holding theupper and lower mold sections 22 and 24 together.

At the same time, the closing speed of the cylinders 42 and 44 is slowedto the required forming speed. Forming speed is determined by trial anderror and differs based on part geometry and LPMC formulation.

The upper mold section 24 continues to move towards the lower moldsection 22 until the mold cavity 25 is closed. This means that eitherthe upper mold section 24 has closed onto the lower mold section 22 withstopping blocks 37 (if used), or the upper mold section 24 has closedagainst the LPMC material trapped in the mold cavity between the upperand lower mold sections. Once the mold is closed, the “cure time”duration is started.

The cure time is dependent on the thickness of the part beingmolded—usually between 60 to 90 seconds per 0.125″ (3 mm) of thickness.Following the cure cycle completion, a command to open the mold set willbe issued by the PLC 56.

Fluid is evacuated from retraction chambers 62 and 68 of the activationhydraulic cylinders 42 and clamping hydraulic cylinders 44 whilesimultaneously being pumped into the extension chambers 64 and 70. Thetransfer of fluid causes the upper mold section 24 to separate from thelower mold section 22 to a pause position (the same pause position asfor the closing phase). At this position, the rod end slide coupler unit54 is disengaged, the activation hydraulic cylinder 42 extends, liftingthe upper mold section 24 to a position that allows removal of themolded part. Simultaneous with the activation hydraulic cylinder 42being extended to open the mold sections 22 and 24, the clampingcylinder rod 50 can be retracted to increase accessibility if required.FIG. 9 illustrates the process showing the mold set in an open/readyposition, a closed molding position and a part removal positionrespectively. In an embodiment that does not include a clampinghydraulic cylinder 44, the steps in the above method would applyexcluding the steps related to the clamping hydraulic cylinder 44.

The above-described embodiments of the present invention are providedpurely for purposes of illustration. Many other variations,modifications, and applications of the invention may be made.

1. An apparatus for compression molding a charge of material into a workpiece comprising: a mold set including a first mold section and a secondmold section; at least one activation cylinder mounted to one of saidfirst and second mold sections, said at least one activation cylinderbeing adapted for extending and retracting a first cylinder rod, saidcylinder rod slidably extending through an aperture in said one moldsection and having an end attached to the other of said first and secondmold sections; and a source of heat for the mold set.
 2. The apparatusof claim 1 wherein said at least one activation cylinder comprises ahydraulic cylinder having extension and retraction chambers eachconnected to a controllable source of pressurized hydraulic fluid. 3.The apparatus of claim 1, wherein said source of heat for said mold setcomprises steam.
 4. The apparatus of claim 1, wherein said source ofheat for the mold set comprises hot oil.
 5. The apparatus of claim 1,wherein said source of heat for the mold set comprises resistance heat.6. The apparatus of claim 1, further comprising at least one clampingcylinder mounted to one of said first and second mold sections, said atleast one clamping cylinder being adapted for extending and retracting asecond cylinder rod having a second end releasably mounted to the otherof said first and second mold sections.
 7. The apparatus of claim 6wherein said at least one clamping cylinder comprises a hydrauliccylinder having extension and retraction chambers each connected to acontrollable source of pressurized hydraulic fluid.
 8. The apparatus ofclaim 1, further including a computer control system connected to thecompression molding apparatus to control the mold process and insurethat said first and second mold sections remain substantially parallelto each other during operation.
 9. The apparatus of claim 8 furthercomprising linear transducers encased in said activation cylinders,wherein said transducers transmit continuous linear position data tosaid computer control system, and wherein said computer control systeminterprets incoming data from said at least one activation cylinder andmonitors and controls hydraulic fluid flow into and out of saidretraction and extension chambers.
 10. The apparatus of claim 7 furthercomprising linear transducers encased in the activation cylinders,wherein said transducers transmit continuous linear position data to acomputer control system, and wherein said computer control systeminterprets incoming data from said at least one activation cylinder andsaid at least one clamping cylinder and monitors and controls hydraulicfluid flow into and out of said retraction and extension chambers. 11.The apparatus of claim 1, wherein said first and second mold sectionsare comprised of a plurality of individual plates connected together.12. The apparatus of claim 1, wherein said first and second moldsections are comprised of a plurality of solid steel bar-stock piecesconnected together.
 13. The apparatus of claim 6, wherein said first andsecond mold sections are comprised of a plurality of individual platesconnected together.
 14. The apparatus of claim 6, wherein said first andsecond mold sections are comprised of a plurality of bar-stock piecesconnected with together.
 15. The apparatus of claim 1, wherein saidfirst mold section and second mold section in a closed position have aninterior surface that defines a mold cavity.
 16. The apparatus of claim1 further comprising support pillars affixed to one of said first andsecond mold sections.
 17. The apparatus of claim 1, wherein said atleast one activation cylinder is arranged on a periphery of said moldset.
 18. The apparatus of claim 1, wherein said at least one activationcylinder is positioned substantially in the center of said mold set. 19.The apparatus of claim 6, wherein said at least one activation cylinderand said at least one clamping cylinder are arranged on a periphery ofsaid mold set.
 20. The apparatus of claim 19, wherein said at least oneactivation cylinder and said at least one clamping cylinder are arrangedin opposing orientation to each other.
 21. The apparatus of claim 19,wherein said at least one activation cylinder and said at least oneclamping cylinder are arranged in an alternating layout.
 22. Theapparatus of claim 1, wherein one of said first and second mold sectionsincludes a plurality of stopping blocks.
 23. The apparatus of claim 1,wherein the charge of material is molded at a force of 75 to 350 psi.24. The apparatus of claim 1, wherein said mold set includesreinforcement plates attached along an exterior surface of said moldset.
 25. The apparatus of claim 6, wherein said mold set includesreinforcement plates attached along an exterior surface of said moldset.